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Original question:

BQ28Z610: changing the DesignCapacity parameter

BQ28Z610: Change resistor to PTC

Jeff Xie
Intellectual 1780 points
Part Number: BQ28Z610

Hi team,

According to the requirements of explosion-proof safety. the volume of series resistors of PACK, VC1 and VC2 is too large. In order to reduce the volume of the original, we intend to make the following changes:

1. The resistance of PACK is changed to 2.2 ohms in series with a 50mA PTC instead (PTC cold resistance is about 4 ohms)

2. The resistance of VC2 is changed to 2.2 ohms in series with a 50mA PTC instead (PTC cold resistance is about 4 ohms)

3. In addition, in order to avoid battery overdischarge, a controllable switch is added to the VC2 foot when the battery voltage is less than 6.0V. Cut off the power supply of VC2 to make the electric quantifier enter the power saving mode.

After making these changes, does it have any effect on the work of the BQ28Z610? If there is any influence, can it be corrected by software? Below is the shcamatic

  • 0
    TI__Mastermind 42535 points
    Your design can work with a few points to note

    1. Your PTC must be very linear between 0 to 80 or 100C. This is because VC2 is also a cell balancing input. The balancing timer calculation depends on the external resistance used.
    2. There may be slight variation in gauging but this really should not affect you at normal temperatures, however the fw can't correct for it as it assumes the circuit is static. If your operating range is -10 to 50C, you should mostly be OK.
    3. choose a PTC that can handle the cell balancing currents and will not heat up because of the cell balancing currents
    4. if you want to cut off at 6V, please make sure that your terminate voltage is at least 6200mV or 6400mV.